1. Field of the Invention
The invention relates to three-dimensional scanning, and more particularly to techniques for resuming a three-dimensional scan after losing data acquisition.
2. Description of the Related Art
A wide range of techniques exist for acquiring three-dimensional data from a subject. These techniques range from techniques using structured laser illumination or other controlled stimulus (such as x-rays, ultrasound, or magnetic resonance) to techniques that operate directly on video data captured from one or more cameras. While many criteria can be devised for sorting and comparing these techniques, one broad category employs continuous scanning in which incremental three-dimensional data is acquired and assembled into a full three-dimensional model.
In this latter category, regardless of the particular sensing technology, a scanning process can be divided into abstract steps of incremental data capture, incremental derivation of three-dimensional data, and registration of the incremental data to a common coordinate system. The final registration step brings the incremental data together into a single three-dimensional model of a scan subject. Typical implementations separate acquisition from registration, with registration being performed in a post-processing step after completion of the data acquisition. While this permits relatively exhaustive processing, it poses a significant disadvantage because accuracy and completeness of the overall scan cannot be evaluated until after the scan has been terminated. Unrecoverable errors or gaps in incremental data cannot be identified and fixed without initiating a new scan—possibly a full scan to completely replace the defective results. In commercial applications, this may create delays and inconvenience that increase the effective cost of scanning.
In certain instances, recovery of lost or unusable scan segments may be addressed by using robotics, independent references, or other techniques that can reliably position a scanning device within a global coordinate system. In addition to imposing further equipment costs, this approach can only be used to continue a previous scan if the subject of the scan has also retained its position and orientation within the same global coordinate system.
There remains a need for processing techniques that identify and aid in recovery from errors in incremental scans. There also remains a need for real time feedback systems to support recovery from a lost scanning sequence while the scan is in progress.